The main aim of this project is to provide a clearer understanding of the expression and modulation of two neuroactive substances that are expressed by a cell population. The cell populations to be studied are those that derive from the neural crest, and in particular those phenotypes present in the sympatho adrenal branch of the peripheral nervous system. Most of these cells differentiate from neural crest precursors into neurons chromaffin cells that synthesize a "classical" neurotransmitter together with one or more neuropeptides. Environmental factors have been shown to determine and modulate the acquisition and expression of the neurotransmitter properties, however, little is known about the factors that affect the co-expression of a particular neuropeptide or about their influence on the maintenance or plasticity of the neurotransmitter/neuropeptide phenotype. Cultures of undifferentiated neural crest and of embryonic sympathetic ganglia and adrenal gland will be used to test the environmental influence on the phenotypic expression at the initial differentiation step and on the modulation of already expressed characteristics, respectively. Immunocytochemical and neurochemical techniques will be used to identify and quantify the number of cells showing different phenotypes. Radioimmunoassay will be used to quantify the amount of neuropeptides and incorporation of radioactive precursors will be used as a measure of neurotransmitter expression. The results should lead to a better understanding of the expression of neurotransmitters, neuropeptides and peptide hormones and of the processes of differentiation and plasticity in cells of the nervous and endocrine systems.